1. Field of the Invention
The present invention refers to an apparatus for hot-briquetting iron sponge, comprising a gravity feeder which comprises a feed shaft and regulating means and which supplies material in dosed quantity to the moulding gap of a roller press.
2. Background
For the purpose of hot-briquetting iron sponge and flue dusts, material feeders provided with a feed shaft are normally used, said feed shaft being directed towards the moulding gap of a roller press and having arranged therein a preforming screw. The preforming screw serves as a means for conveying the material and it guarantees that the flow of material to the roller press can be controlled as desired. In addition, pressure is applied to the material in the inlet area of the roller press by means of the preforming screw. The material is conveyed to the moulding gap of the roller press by means of the preforming screw and urged, in a precompacted condition, into briquetting moulds of the roller press. This is necessary for obtaining a briquette density of more than 5 g per cubic centimetre.
It is disadvantageous that a hot-briquetting apparatus provided with a screw-type material feeder can only be used for maximum operating temperatures of from 700.degree. to 750.degree. C. New iron ore reduction processes, however, necessitate temperatures of up to 1000.degree. C. in the briquetting press for further processing the material. This type of material feeder, and especially the preforming screw, are not capable of resisting these temperatures. The material of the screw becomes soft and deforms due to the substantial temperature and pressure loads. Attempts which have been made for cooling the screw proved to be very complicated and expensive from the structural point of view. Moreover, a cooled screw will cool down the material in the area close to the screw to such an extent that it is no longer suitable for the hot-briquetting process.
In connection with a subject matter which belongs to the above-mentioned class of device and which is known from the cold-briquetting process, a gravity feeder is known which converts undersize material with a grain size of up to three millimetres, which can no longer be supplied to an electric furnace directly, into briquettes by pressing. This type of apparatus can, in an disadvantageous manner, only be used for cold-pressing grain sizes up to 3 mm. Coarser materials, occurring e.g. in the form of lump ore and pellets having a size of up to 25 mm in hot-briquetting plants, can thus no longer be processed such that above-mentioned briquetting density is obtained.